This invention relates to blow molding, and in particular it relates to a transfer means for handling a parison in connection with the cold parison technique.
Tubular parisons are formed and heated to a temperature suitable for blow molding in two ways. According to one procedure, a parison is extruded in a hot state and while still hot it is carried over to the blow mold. In accordance with another procedure, the extruded parisons are cooled and/or stored for use at a subsequent time and/or place. This latter procedure is referred to as the "cold parison" procedure because it starts with a cold (i.e., room temperature) parison which must be heated in an oven or the like to a temperature suitable for blow molding after which it must be transferred from the oven to the blow mold. The present invention is concerned in particular with the cold parison procedure and more specifically with the task of transferring a parison which has been heated in an oven from the oven to the blow mold. A suitable method and apparatus for carrying out the cold parison technique is described in detail in commonly owned U.S. Pat. No. 3,765,813, issued Oct. 16, 1973, and the disclosure of which is incorporated by reference herein for details of a typical cold parison technique.
In a parison heating oven such as the type shown in the said patent, the parisons are supported in an upright position on carrier pins as they travel through the oven. The oven is designed and operated such that as the parisons reach the suitable forming temperature they arrive at a discharge station at which a transfer means having some type of gripping structure enters the oven from above through an opening, grips a properly heated parison, removes the parison upwardly out of the oven and then transfers the parison laterally to the blow mold whereat the parison is lowered. In the type of operation with which the said previous patent is concerned, the parison is stretched for biaxial orientation by gripping the lower end of the parison in the vicinity of the blow mold and then raising the gripping means. Hence, the gripper means has a dual function of at least gripping the parison at the oven and removing it therefrom and also assisting in stretching of the parison.
Certain problems have been encountered in carrying out these functions with previously known gripper means. One problem has been that on numerous occasions as the parisons within the oven arrive at the discharge station they are tilted to one side rather than in the desired upright position. Previously known gripper means which were designed primarily for receiving and gripping a properly positioned upright parison would tend to either miss this parison altogether or pick it up in a tilted condition. In either case the result would be a reject. If the parison were not picked up at all it would have to be removed and recycled; and if the parison were picked up with a tilted orientation it would arrive at the blow mold improperly oriented so that it would not be gripped and stretched in the desired manner.
Another difficulty has concerned the type of known gripper means having a pair of opposed planar jaws. This type of gripper means closes the upper end of the parison by flattening the upper end. When the parison is gripped in this manner, as the gripper means moves upwardly during the stretching operation, stretching will not be applied uniformly about the periphery of the parison.
Thus, there exists a need for a new and improved means for handling a parison in connection with the cold parison technique.